/*
 * Based on JUEL 2.2.1 code, 2006-2009 Odysseus Software GmbH
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.activiti.engine.impl.javax.el;

import java.beans.FeatureDescriptor;
import java.util.Iterator;
import java.util.Map;

/**
 * Defines property resolution behavior on instances of java.util.Map. This resolver handles base
 * objects of type java.util.Map. It accepts any object as a property and uses that object as a key
 * in the map. The resulting value is the value in the map that is associated with that key. This
 * resolver can be constructed in read-only mode, which means that isReadOnly will always return
 * true and {@link #setValue(ELContext, Object, Object, Object)} will always throw
 * PropertyNotWritableException. ELResolvers are combined together using {@link CompositeELResolver}
 * s, to define rich semantics for evaluating an expression. See the javadocs for {@link ELResolver}
 * for details.
 */
public class MapELResolver extends ELResolver {
    private final boolean readOnly;

    /**
     * Creates a new read/write MapELResolver.
     */
    public MapELResolver() {
        this(false);
    }

    /**
     * Creates a new MapELResolver whose read-only status is determined by the given parameter.
     */
    public MapELResolver(boolean readOnly) {
        this.readOnly = readOnly;
    }

    /**
     * If the base object is a map, returns the most general type that this resolver accepts for the
     * property argument. Otherwise, returns null. Assuming the base is a Map, this method will
     * always return Object.class. This is because Maps accept any object as a key.
     *
     * @param context The context of this evaluation.
     * @param base    The map to analyze. Only bases of type Map are handled by this resolver.
     * @return null if base is not a Map; otherwise Object.class.
     */
    @Override
    public Class<?> getCommonPropertyType(ELContext context, Object base) {
        return isResolvable(base) ? Object.class : null;
    }

    /**
     * If the base object is a map, returns an Iterator containing the set of keys available in the
     * Map. Otherwise, returns null. The Iterator returned must contain zero or more instances of
     * java.beans.FeatureDescriptor. Each info object contains information about a key in the Map,
     * and is initialized as follows:
     * <ul>
     * <li>displayName - The return value of calling the toString method on this key, or "null" if
     * the key is null</li>
     * <li>name - Same as displayName property</li>
     * <li>shortDescription - Empty string</li>
     * <li>expert - false</li>
     * <li>hidden - false</li>
     * <li>preferred - true</li>
     * </ul>
     * In addition, the following named attributes must be set in the returned FeatureDescriptors:
     * <ul>
     * <li>{@link ELResolver#TYPE} - The return value of calling the getClass() method on this key,
     * or null if the key is null.</li>
     * <li>{@link ELResolver#RESOLVABLE_AT_DESIGN_TIME} - true</li>
     * </ul>
     *
     * @param context The context of this evaluation.
     * @param base    The map to analyze. Only bases of type Map are handled by this resolver.
     * @return An Iterator containing zero or more (possibly infinitely more) FeatureDescriptor
     * objects, each representing a key in this map, or null if the base object is not a
     * map.
     */
    @Override
    public Iterator<FeatureDescriptor> getFeatureDescriptors(ELContext context, Object base) {
        if (isResolvable(base)) {
            Map<?, ?> map = (Map<?, ?>) base;
            final Iterator<?> keys = map.keySet().iterator();
            return new Iterator<FeatureDescriptor>() {
                public boolean hasNext() {
                    return keys.hasNext();
                }

                public FeatureDescriptor next() {
                    Object key = keys.next();
                    FeatureDescriptor feature = new FeatureDescriptor();
                    feature.setDisplayName(key == null ? "null" : key.toString());
                    feature.setName(feature.getDisplayName());
                    feature.setShortDescription("");
                    feature.setExpert(true);
                    feature.setHidden(false);
                    feature.setPreferred(true);
                    feature.setValue(TYPE, key == null ? "null" : key.getClass());
                    feature.setValue(RESOLVABLE_AT_DESIGN_TIME, true);
                    return feature;

                }

                public void remove() {
                    throw new UnsupportedOperationException("cannot remove");
                }
            };
        }
        return null;
    }

    /**
     * If the base object is a map, returns the most general acceptable type for a value in this
     * map. If the base is a Map, the propertyResolved property of the ELContext object must be set
     * to true by this resolver, before returning. If this property is not true after this method is
     * called, the caller should ignore the return value. Assuming the base is a Map, this method
     * will always return Object.class. This is because Maps accept any object as the value for a
     * given key.
     *
     * @param context  The context of this evaluation.
     * @param base     The map to analyze. Only bases of type Map are handled by this resolver.
     * @param property The key to return the acceptable type for. Ignored by this resolver.
     * @return If the propertyResolved property of ELContext was set to true, then the most general
     * acceptable type; otherwise undefined.
     * @throws NullPointerException if context is null
     * @throws ELException          if an exception was thrown while performing the property or variable resolution.
     *                              The thrown exception must be included as the cause property of this exception, if
     *                              available.
     */
    @Override
    public Class<?> getType(ELContext context, Object base, Object property) {
        if (context == null) {
            throw new NullPointerException("context is null");
        }
        Class<?> result = null;
        if (isResolvable(base)) {
            result = Object.class;
            context.setPropertyResolved(true);
        }
        return result;
    }

    /**
     * If the base object is a map, returns the value associated with the given key, as specified by
     * the property argument. If the key was not found, null is returned. If the base is a Map, the
     * propertyResolved property of the ELContext object must be set to true by this resolver,
     * before returning. If this property is not true after this method is called, the caller should
     * ignore the return value. Just as in java.util.Map.get(Object), just because null is returned
     * doesn't mean there is no mapping for the key; it's also possible that the Map explicitly maps
     * the key to null.
     *
     * @param context  The context of this evaluation.
     * @param base     The map to analyze. Only bases of type Map are handled by this resolver.
     * @param property The key to return the acceptable type for. Ignored by this resolver.
     * @return If the propertyResolved property of ELContext was set to true, then the value
     * associated with the given key or null if the key was not found. Otherwise, undefined.
     * @throws ClassCastException   if the key is of an inappropriate type for this map (optionally thrown by the
     *                              underlying Map).
     * @throws NullPointerException if context is null, or if the key is null and this map does not permit null keys
     *                              (the latter is optionally thrown by the underlying Map).
     * @throws ELException          if an exception was thrown while performing the property or variable resolution.
     *                              The thrown exception must be included as the cause property of this exception, if
     *                              available.
     */
    @Override
    public Object getValue(ELContext context, Object base, Object property) {
        if (context == null) {
            throw new NullPointerException("context is null");
        }
        Object result = null;
        if (isResolvable(base)) {
            result = ((Map<?, ?>) base).get(property);
            context.setPropertyResolved(true);
        }
        return result;
    }

    /**
     * If the base object is a map, returns whether a call to
     * {@link #setValue(ELContext, Object, Object, Object)} will always fail. If the base is a Map,
     * the propertyResolved property of the ELContext object must be set to true by this resolver,
     * before returning. If this property is not true after this method is called, the caller should
     * ignore the return value. If this resolver was constructed in read-only mode, this method will
     * always return true. If a Map was created using java.util.Collections.unmodifiableMap(Map),
     * this method must return true. Unfortunately, there is no Collections API method to detect
     * this. However, an implementation can create a prototype unmodifiable Map and query its
     * runtime type to see if it matches the runtime type of the base object as a workaround.
     *
     * @param context  The context of this evaluation.
     * @param base     The map to analyze. Only bases of type Map are handled by this resolver.
     * @param property The key to return the acceptable type for. Ignored by this resolver.
     * @return If the propertyResolved property of ELContext was set to true, then true if calling
     * the setValue method will always fail or false if it is possible that such a call may
     * succeed; otherwise undefined.
     * @throws NullPointerException if context is null.
     * @throws ELException          if an exception was thrown while performing the property or variable resolution.
     *                              The thrown exception must be included as the cause property of this exception, if
     *                              available.
     */
    @Override
    public boolean isReadOnly(ELContext context, Object base, Object property) {
        if (context == null) {
            throw new NullPointerException("context is null");
        }
        if (isResolvable(base)) {
            context.setPropertyResolved(true);
        }
        return readOnly;
    }

    /**
     * If the base object is a map, attempts to set the value associated with the given key, as
     * specified by the property argument. If the base is a Map, the propertyResolved property of
     * the ELContext object must be set to true by this resolver, before returning. If this property
     * is not true after this method is called, the caller can safely assume no value was set. If
     * this resolver was constructed in read-only mode, this method will always throw
     * PropertyNotWritableException. If a Map was created using
     * java.util.Collections.unmodifiableMap(Map), this method must throw
     * PropertyNotWritableException. Unfortunately, there is no Collections API method to detect
     * this. However, an implementation can create a prototype unmodifiable Map and query its
     * runtime type to see if it matches the runtime type of the base object as a workaround.
     *
     * @param context  The context of this evaluation.
     * @param base     The map to analyze. Only bases of type Map are handled by this resolver.
     * @param property The key to return the acceptable type for. Ignored by this resolver.
     * @param value    The value to be associated with the specified key.
     * @throws ClassCastException           if the class of the specified key or value prevents it from being stored in this
     *                                      map.
     * @throws NullPointerException         if context is null, or if this map does not permit null keys or values, and the
     *                                      specified key or value is null.
     * @throws IllegalArgumentException     if some aspect of this key or value prevents it from being stored in this map.
     * @throws PropertyNotWritableException if this resolver was constructed in read-only mode, or if the put operation is
     *                                      not supported by the underlying map.
     * @throws ELException                  if an exception was thrown while performing the property or variable resolution.
     *                                      The thrown exception must be included as the cause property of this exception, if
     *                                      available.
     */
    @Override
    @SuppressWarnings("unchecked")
    public void setValue(ELContext context, Object base, Object property, Object value) {
        if (context == null) {
            throw new NullPointerException("context is null");
        }
        if (isResolvable(base)) {
            if (readOnly) {
                throw new PropertyNotWritableException("resolver is read-only");
            }
            ((Map) base).put(property, value);
            context.setPropertyResolved(true);
        }
    }

    /**
     * Test whether the given base should be resolved by this ELResolver.
     *
     * @param base     The bean to analyze.
     * @param property The name of the property to analyze. Will be coerced to a String.
     * @return base instanceof Map
     */
    private final boolean isResolvable(Object base) {
        return base instanceof Map<?, ?>;
    }
}
